[Bug 81476] three monitors on two radeon cards works with some layouts not others

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=81476

--- Comment #13 from Ian! D. Allen <idallen at idallen.ca> ---
(In reply to comment #11)
> Does this kernel patch help?

Not with my problem.

1. It doesn't fix the bug and make my desktop work across three monitors.
2. It doesn't prevent all the configurations that can trigger the bug.
3. It does prevent some valid configurations that used to work before.

With your patch, xrandr shows the new smaller screen maximum:

    Screen 0: minimum 320 x 200, current 4096 x 1200, maximum 4096 x 4096
    DVI-0 connected 1600x1200+0+0 
    DVI-1 connected 1600x1200+1600+0 
    DVI-1-2 connected 1600x1200+2496+0 
    DVI-1-3 disconnected

The +2432 offset still works fine across three monitors, as it did before:

    xrandr --output DVI-1-2 --pos 2432x0 --auto

Offsets from +2433 to +2496 are still allowed and still trigger the bug and
cause video crap on the first two monitors, just as they did before.

Offsets above +2496 are now prohibited due to the new smaller screen maximum,
even though I know they would work if I rotated or inverted the first two
monitors.

Your patch doesn't fix the bug.  It does prevent me from using the actual
available screen resolution, should I want to invert or rotate the first two
monitors.  Functionality is lost.

I gather you don't know how to fix the bug, so you're instead trying to limit
the inputs so as not to not let people trigger it?

You said "Rotation uses an additional buffer for each display".  I guess I'll
have to go through the code and find out how to make the non-inverted outputs
use the same type of buffering as the inverted outputs for widths above 4064. 
That should work.

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